Examples of the winding component of related art include a power transformer used in an electric automobile, a large-sized server, and other apparatus and a transformer and a choke coil used in a DC-DC converter.
In general, when the winding component described above is used to carry current of a large magnitude, copper loss occurs in a wire material of which the coil is made and causes a concern about thermal runaway of a ferrite core and degradation in heat resistance of surrounding materials, possibly resulting in a difficulty in thermal formation of the transformer. To avoid the problem, for example, the diameter of an electric wire that forms the coil is increased to lower the electrical resistance so that no copper loss occurs.
To wind an electric wire around the outer circumference of a core, and when a core 25 is, for example, an E-type core, the mid-leg of the core 25 is inserted into a bobbin 21, which is made of an insulating material, and an electric wire t, such as a copper wire, is wound around a tubular winding part 21a of the bobbin 21 to form a coil 23, as shown in FIG. 4. The bobbin 21 needs to ensure insulation between the core 25 and the electric wire t because lead wires 24 are drawn outward through notches 22, which are formed in flanges 21b. Further, to attach a winding component 20 to an enclosure, insulation between the lead wires 24, which are drawn from the coil 23 wound around the bobbin 21, and the enclosure needs to be ensured.
To this end, for example, the following methods of related art have been proposed: a method for providing a wall 26 between the notches 22 formed in the flanges 21b of the bobbin 21 and the core 25 and drawing the lead wires 24 with the lead wires 24 separated from the wall 26 by a longest possible distance, as shown in FIG. 4A; a method for covering each of the notches 22 formed in the flanges 21b of the bobbin 21 with a resin 27, as shown in FIG. 4B; and a method for putting an insulating tube 28 over each of the lead wires 24, as shown in FIG. 4C.
When the winding component 20 is used to carry current of a large magnitude, however, particularly when current of a large magnitude ranging from 10 to 30 A or higher flows, the thickness of the electric wire needs to be increased to suppress copper loss. For example, when a litz wire formed of a large number of twisted wires, is used, the final wire diameter ranges from 2 to 3 mm. Therefore, in the method of related art shown in FIG. 4A for providing the wall 26 between the notches 22 formed in the flanges 21b of the bobbin 21 and the core 25 and drawing the lead wires 24 with the lead wires 24 separated from the wall 26 by a longest possible distance, each of the lead wires 24 has a large bending radius, and the core 25 and the lead wire 24 cannot desirably be separated from each other by a sufficiently large creepage distance.
In the method of related art shown in FIG. 4B for covering each of the notches 22 formed in the flanges 21b of the bobbin 21 with the resin 27, when the resin 27 covers each of the notches 22, size limitation is imposed from general implementation reasons. A sufficiently large space that accommodates a thick electric wire cannot therefore be provided. In the wire winding process, for example, the lead wires 24 lift up or disengage from the bobbin 21, which means that the operability and product quality are undesirably compromised.
It is conceivable that a fixture or any other tool is used to hold the lead wires 24 drawn through the notches 22 formed in the flanges 21b before the wire winding operation is performed. However, the portion where each of the notches 22 is covered with the resin 27 is typically narrow, and it is difficult to provide a space that accommodates the fixture. Further, when the winding component 20 is directly disposed in the enclosure, the insulating distance between the lead wire 24 that is drawn downward and the enclosure is undesirably insufficient.
When high withstand voltage is required between the core 25 and the coil 23, for example, when a withstand voltage of AC 2000 V is required, the winding component is so typically designed and manufactured that a creepage distance of at least several millimeters between the lead wires 24 and the core 25 is ensured. Further, when the winding component 20 is required to comply with a safety standard, it is necessary to provide a large creepage distance between the lead wires 24 and the core 25. For example, creepage distances required by a variety of standards in a case where the operating voltage is 400 V are shown in the following Table 1. Table 1 shows safety standards required for a winding component operating at a voltage of 400 V.
TABLE 1OperatingvoltageCreepage distanceSafety standard400 V2.8 mm or greaterIEC 60664, basic insulation, degree ofcontamination 2, material group II5.6 mm or greaterIEC 60664, reinforced insulation, degreeof contamination 2, material group II6.4 mm or greaterUL2202
As described above, in the winding component 20 that requires high withstand voltage between the core 25 and the coil 23, the method for putting the insulating tube 28 over each of the lead wires 24 has been used, as shown in FIG. 4C. In this method of related prior art, the lead wires 24 are drawn through the notches 22 formed in the flanges 21b of the bobbin 21 with the insulating tube 28 put over each of the lead wires 24.
In the winding component 20 that carries current of a large magnitude, however, since the electric wire t itself becomes thick, operation of putting the insulating tube 28 over the electric wire t is time-consuming operation, and an insulating tube 28 that satisfies reinforce insulation is expensive, undesirably resulting in an increase in manufacturing cost.
Further, since the insulating tube 28 itself also becomes thick, and winding the insulating tube 28 along with the coil 23 thickens the wound coil 23, which makes it difficult to bend the lead wires 24 drawn through the notches 22, resulting in a problem of restriction of the flexibility in routing the lead wires.